1. Field of the Invention
The present invention relates to a wireless communication system. More particularly, the present invention relates to a method and apparatus for transmitting/receiving a reference signal for positioning in a wireless communication system.
2. Description of the Related Art
A Location-Based Service (LBS), which provides an estimation of a Mobile Station (MS) location in a wireless communication system, may be generally divided into network-based technology and handset-based technology. A typical example of handset-based technology is a Global Positioning System (GPS). The GPS technology provides very accurate positioning, but has a problem in that it cannot function properly or its positioning accuracy is lowered in a crowded area or an indoor environment. The network-based technology uses a wireless communication network to provide an estimation of an MS location by measuring locations of Base Stations (BSs) and measuring Time Difference Of Arrival (TDOA) or Angle Of Arrival (AOA). Also, the network-based technology may be subdivided into technology using Downlink (DL) and technology using Uplink (UL).
In general, each BS in a wireless communication system periodically transmits a reference signal with a unique pattern, that is, a preamble signal, a pilot signal, or a beacon signal, and thus the location of an MS can be estimated based on the reference signal.
Preambles of Orthogonal Frequency Division Multiplexing (OFDM) systems, for example, the preamble of an Institute of Electrical and Electronics Engineers (IEEE) 802.16e system and the Secondary Advance (SA) preamble of the IEEE 802.16m system, are also designed as to use different subcarriers according to sectors, thereby maintaining orthogonality between the sectors. However, interference due to preamble signals transmitted from the same sector of other BSs is still present, and interference is also present because orthogonality cannot be maintained due to the effect of multipath fading. On account of this, there is a problem in that an MS cannot receive preamble signals from neighbor BSs adjacent thereto, which increases an error in positioning.
The inability to receive neighbor BS signals due to interference, that is, the so-called “hearability” problem, similarly occurs in Code Division Multiple Access (CDMA) networks. To address this hearability problem, the 3rd Generation Partnership Project (3GPP) has proposed Idle Period Downlink (IPDL) technology in which a specific BS suspends all DL channel transmissions so that an MS can receive pilot signals of other BSs. As a similar solution in an OFDM system, a method has been proposed to improve the reception performance of a preamble signal by allocating a specific subframe for wireless positioning purposes and allowing neighbor BSs to transmit a preamble signal without performing data communication in the specific subframe. However, such suspension of data communication deteriorates service quality and causes a significant problem with a Hybrid Automatic Retransmission reQuest (HARQ) operation. In particular, when synchronous HARQ is used for UL data communication, as in the IEEE 802.16m system, an Acknowledge/Not-Acknowledge (ACK/NACK) message transmitted in the DL has direct influence on the overall HARQ timing, and thus the overall DL data communication is deteriorated.